The protein encoded by this gene is a member of the beta chemokine receptor family. It is predicted to be a seven transmembrane protein similar to G protein-coupled receptors. Chemokines and their receptors are key regulators of thymocyte migration and maturation in normal and inflammatory conditions. The specific ligand of this receptor is CCL25. It has been found that this gene is differentially expressed by T lymphocytes of small intestine and colon, suggested a role in thymocyte recruitment and development that may permit functional specialization of immune responses in different segments of the gastrointestinal tract. This gene is mapped to the chemokine receptor gene cluster region. Two alternatively spliced transcript variants have been described.
^Zaballos A, Gutierrez J, Varona R, Ardavin C, Marquez G (Jun 1999). "Cutting edge: identification of the orphan chemokine receptor GPR-9-6 as CCR9, the receptor for the chemokine TECK". J Immunol. 162 (10): 5671–5. PMID10229797.
Yu CR, Peden KW, Zaitseva MB, et al. (2000). "CCR9A and CCR9B: two receptors for the chemokine CCL25/TECK/Ck beta-15 that differ in their sensitivities to ligand.". J. Immunol. 164 (3): 1293–305. doi:10.4049/jimmunol.164.3.1293. PMID10640743.
Maho A, Bensimon A, Vassart G, Parmentier M (2000). "Mapping of the CCXCR1, CX3CR1, CCBP2 and CCR9 genes to the CCR cluster within the 3p21.3 region of the human genome.". Cytogenet. Cell Genet. 87 (3-4): 265–8. doi:10.1159/000015443. PMID10702689.
Papadakis KA, Prehn J, Nelson V, et al. (2000). "The role of thymus-expressed chemokine and its receptor CCR9 on lymphocytes in the regional specialization of the mucosal immune system.". J. Immunol. 165 (9): 5069–76. doi:10.4049/jimmunol.165.9.5069. PMID11046037.
Papadakis KA, Landers C, Prehn J, et al. (2003). "CC chemokine receptor 9 expression defines a subset of peripheral blood lymphocytes with mucosal T cell phenotype and Th1 or T-regulatory 1 cytokine profile.". J. Immunol. 171 (1): 159–65. doi:10.4049/jimmunol.171.1.159. PMID12816994.
Qiuping Z, Qun L, Chunsong H, et al. (2003). "Selectively increased expression and functions of chemokine receptor CCR9 on CD4+ T cells from patients with T-cell lineage acute lymphocytic leukemia.". Cancer Res. 63 (19): 6469–77. PMID14559839.
Babu S, Blauvelt CP, Kumaraswami V, Nutman TB (2005). "Chemokine receptors of T cells and of B cells in lymphatic filarial infection: a role for CCR9 in pathogenesis.". J. Infect. Dis. 191 (6): 1018–26. doi:10.1086/427658. PMID15717282.
Sen Y, Yongyi B, Yuling H, et al. (2005). "V alpha 24-invariant NKT cells from patients with allergic asthma express CCR9 at high frequency and induce Th2 bias of CD3+ T cells upon CD226 engagement.". J. Immunol. 175 (8): 4914–26. doi:10.4049/jimmunol.175.8.4914. PMID16210593.
Nagakubo D, Jin Z, Hieshima K, et al. (2007). "Expression of CCR9 in HTLV-1+ T cells and ATL cells expressing Tax.". Int. J. Cancer. 120 (7): 1591–7. doi:10.1002/ijc.22483. PMID17205512.
Olaussen RW, Karlsson MR, Lundin KE, et al. (2007). "Reduced chemokine receptor 9 on intraepithelial lymphocytes in celiac disease suggests persistent epithelial activation.". Gastroenterology. 132 (7): 2371–82. doi:10.1053/j.gastro.2007.04.023. PMID17570212.